Method of treating cellulose acetate



Patented May 28, 1935 UNITED STATES METHOD on TREATING oELLULos ACETATERichard Miiller. and Martin Schenck, Mannheim, and Wilhelm Wirbatz,Mannheim-Waldhof, Germany, assignors to C. F. Boehringer & Soehne G. in.b. H., Mannheim-Waldhof, Germany No Drawing. Application June'lf i,1930, Serial No. 461,636. In Austria June 21, 1929 ll Claims. (01.260-102) Our invention'refers to .a treatment of fibri form acetylcelluloses or cellulose acetates of the kind which dissolve inchloroform, whereby I the solubility of these compounds in acetone isaffected me favourable manner.

As is well known to those skilled in the art, when cellulose isacetylized, there is first formed a primary product of acetylizationwhich, before being fit for use in the production of artificial silk andother materials ,must first be converted into a secondary productcontaining less acetic acid and dissolving in acetone. The primaryproduct, While being insoluble in acetone, is soluble in chloroformeither completely or incompletely.

It is to these primary fibriform products which dissolve in chloroformeithter partly or totally that reference is had in the followingspecification and in the claims affixed thereto. They are little adaptedfor technical uses. We have now found that the solubility of theseprimary products can be influenced favourably by acting thereon withcomparatively concentrated and strong acids, if care 'is taken tosuppressby suitable additions the decomposing and dissolving effect 'ofthe acids. By this treatment the products are not aifected invanyunfavourable manner and their fibrous structure is not destroyed.

We have found that by adding to the reaction mixture a salt, an ester orother inorganic or organic substances which are inert with respect tothe cellulose acetate and the acid and are highly soluble in the acid,in such proportion as to prevent the cellulose acetate from dissolvingduring its conversion to the acetone soluble form, so that by exerting asalting out or precipitating effect on the acetyl cellulose with orwithout a simultaneous reduction of the dissociation of the acids, theyprevent the acetyl cellulose from being dissolved, the action of theconcentrated acids can be nicely regulated. Salting out is a Well-knownphenomena which is produced by highly soluble salts. It is defined byPerry (Chemical Engineers Handbook, Mc- Graw Hill 00., 1934, page 564)as follows:

When an electrolyte (salt) is added to an aqueous solution of anon-electrolyte, as hydrogen, ether, or succinic acid, the solubility ofthe latter is greatly diminished. The mutual solubility of two liquidssuch as ether and water is reduced by the addition of such a salt assodium chloride or sodium sulfate. This phenomenon is called the saltingout effect In accordance with the mode of proceeding in each individualcase including the character of the acids and additions used, theirconcentration and. relative proportions, the temperature etc. theproductwill after a predetermined periodbec'ome solublein acetone eithercompletely or incompletely.

Example 2 If a similar material is treated during some days at ordinarytemperature with a 95% nitric acid saturated with ammonium nitrate, theproduct has become soluble in acetone while its fibrousstructure has notbeen changed.

Example 3 Fibrous cellulose acetate soluble in chloroform is introducedinto a mixture of 9 parts by volume of a 96% phosphoric acid, 1 part ofa 96% sulfuric acid and 23 parts cyclohexanol acetate. After the lapseof several days the product has become soluble in acetone. The reactioncan be expedited by slightly heating the mixture.

Example 4 Fibrous cellulose acetate soluble in chloroform is treated atordinary temperature during two days with a mixture of 10 parts byvolume of a 96-97% phosphoric acid and 1'7 parts by volume cyclohexanolacetate with the result, that the acetyl cellulose has become soluble inacetone.

Example 5 Fibrous cellulose acetate soluble in chloroform is introducedinto a mixture of 80 parts of a 96-97% phosphoric acid and 16 partsammonium sulfate. After the lapse of 2-3 days the product has becomesoluble in acetone.

Other buffer salts which produce a salting out effect and which areuseful in our process, for preventing the cellulose acetate fromdissolving in the acid until the acetone-soluble stage is 55 reached,are potassium nitrate and calcium nitrate.

Various changes may be made in the details disclosed in the foregoingspecification without departing from the invention or sacrificing theadvantages thereof.

We claim:-

1. The method of treating fibriform cellulose acetate soluble inchloroform but insoluble in acetone to render it soluble in acetone andyet preserve its fibrous structure, which comprises subjecting saidacetate in solid fibrous form to a conversion bath of a concentratedmineral acid substantially saturated with a highly soluble buffersubstance inert towards both the acid and the acetate but producing aprecipitating effect on the acetate and acting to prevent the dissolvingof said acetate by said bath, the action of the bath being continueduntil the acetate has been rendered soluble in acetone.

2. The method of claim 1 wherein said substance is a highly solubleinorganic salt.

3. The method of claim 1 wherein said substance is a nitrate.

4. The method of claim 1 wherein said substance is an ammonium salt.

5. The method of claim 1 wherein said substance is a sulfate. 1

6. The method of treating fibriform cellulose acetate soluble inchloroform but insoluble in acetone to render it soluble in acetone andyet preserve its fibrous structure, which comprises subjecting saidacetate in solid fibrous form to a conversion bath of a concentratedmineral acid substantially saturated with a salt inert towards both theacid and the acetate but producing a precipitating effect on the acetateand acting to prevent the dissolving of said acetate by said bath, theaction of the bath being continued until the acetate has been renderedsoluble in acetone, said salt being selected from the group consistingof calcium nitrate, potassium nitrate, ammonium nitrate, ammoniumsulphate and secondary ammonium phosphate.

7. The method of claim 6 wherein said substance is secondary ammoniumphosphate.

8. The method of claim 6 wherein said substance is ammonium nitrate.

9. The method of claim 6 wherein said substance is ammonium sulphate.

RICHARD MI'JLLER. MARTIN SCHENCK. WILHELM WIRBATZ.

